Adaptor protein 2 sigma subunit (AP2S1) variants associated with neurodevelopmental disorders

Adaptor-Related Protein Complex 2 Sigma-1 Subunit (AP2S1) encodes AP2σ2, which forms part of the heterotetrameric AP2 complex that is composed of α, β2, μ2, and σ2 subunits and has a pivotal role in clathrin-mediated endocytosis (CME). AP2S1 variants involving the Arg15 residue are associated with familial hypocalciuric hypercalcaemia type 3 (FHH3). Here, we report 5 different AP2S1 variants (AP2σ2: p.Arg10Trp, p.Arg10Gln, p.Lys18Glu, p.Lys18Asn and p.Arg61His) in 26 patients with neurodevelopmental delay, of whom >70% had epilepsy, 50% had brain abnormalities, and none had hypercalcaemia. All 5 variants decreased cell viability, 4 reduced CME transferrin uptake, and 4 disrupted interactions with other AP2 complex subunits, thereby affecting AP2 formation. Furthermore, AP2σ2 p.Arg10Trp had reduced interactions with 44 human proteins including intersectin 1, a component required for clathrin-coated pit formation and synaptic vesicle dynamics in neurones. Thus, our results show that AP2σ2 variants may disrupt CME and be associated with neurodevelopmental disorders. ### Competing Interest Statement AB, DAC, JJ and JJK are employees of GeneDx, LLC ### Funding Statement This work was supported by a Wellcome Trust Senior Clinical Investigator Award (RVT), and National Institute for Health Research (NIHR) Oxford Biomedical Research Centre Programme grant. RVT is a Wellcome Trust Investigator and NIHR Senior Investigator. For the purpose of Open Access, the author has applied a CC BY public copyright licence to any Author Accepted Manuscript (AAM) version arising from this submission. We are grateful to the patients and families that participated in this research. The authors are grateful to the participants of the MyCode Community Health Initiative for the use of their genomic and electronic health information. The patient enrolment and exome sequencing for the DiscovEHR study were funded by the Regeneron Genetics Center. We would like to acknowledge the Geisinger-Regeneron DiscovEHR Collaboration for making the genotype data and phenotype available for this project. This research was also made possible through access to data in the National Genomic Research Library, which is managed by Genomics England Limited (a wholly owned company of the Department of Health and Social Care). The National Genomic Research Library holds data provided by patients and collected by the NHS as part of their care and data collected as part of their participation in research. The National Genomic Research Library is funded by the National Institute for Health Research and NHS England. The Wellcome Trust, Cancer Research UK and the Medical Research Council have also funded research infrastructure. Mass spectrometry analysis was performed at the Discovery Proteomics Facility (headed by Roman Fischer) which is part of the TDI MS Laboratory (led by Benedikt Kessler). KGC is Chairholder of the Emil von Behring Chair for Neuromuscular and Neurodegenerative Disorders by CSL Behring. KGC is member of the European Reference Network for Rare Neuromuscular Diseases (ERN EURO-NMD) and of the European Reference Network for Rare Neurological Diseases (ERN-RND). KGC reports no disclosures relevant to the manuscript. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The London Multi-Centre Research Ethics Committee (MREC) gave ethical approval for this work (MREC/02/2/93). Informed consent was obtained from individuals or their family/guardians/parents, using protocols approved by the local and national ethics committees. I confirm that all necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived, and that any patient/participant/sample identifiers included were not known to anyone (e.g., hospital staff, patients or participants themselves) outside the research group so cannot be used to identify individuals. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines, such as any relevant EQUATOR Network research reporting checklist(s) and other pertinent material, if applicable. Yes All data produced in the present study are available upon reasonable request to the authors